The braking action in an automobile is generally caused by forcing a brake shoe against a surface such as the disc rotor attached to a car's axle. The action of the brake piston forcing the hard brake shoe against the rotor can cause a vibration which in turn generates an unpleasant squeal. To avoid this, vibration dampers are positioned on a brake shoe, opposite the friction pad on each side of the rotor within the caliper. Frequently these are physically attached to the brake shoe. Some of these are simply a coating onto the back side of the brake shoe. Others are more sophisticated laminates.
One of the most effective vibration dampers is a metal-to-metal laminate where two metal layers are bonded together by an intermediate visco-elastic layer. These dampers are developed by initially combining the metal-to-metal laminate and coiling this up prior to use. When needed, the laminate is uncoiled, slit to specific widths or "reels," and stamped to form a planar vibration damper which generally corresponds in size to the back side of the brake shoe. They can be physically attached and/or adhesively bonded to the brake shoe or both.
Due to the method of manufacture, the viscoelastic intermediate layer must exhibit high extensional shear. When the laminate is coiled, as well as during portions of the manufacturing process, one layer must move slightly relative to the other layer. Without this extensional shear, the intermediate layer will prevent this movement and cause delamination. Unfortunately, materials with high extensional shear are generally weak and tend to delaminate in use.
Vibration dampers frequently include a plurality of clips which are stamped from the metal laminate and formed. These clips physically attach the damper to the back side of the brake shoe side opposite the friction pad. If the intermediate layer has a low extensional shear, there can be delamination at the clip portion, i.e. the upper and lower metal layers separate. Even if the intermediate layer possesses sufficient extensional shear, it may not be sufficiently strong to prevent delamination of the clip due to high residual metal stress or the clip or tab design. This delamination itself can be a cause of vibration and noise. Thus, the clips themselves, the design, and the method of manufacture have mandated that the intermediate layer have high extensional shear which, in turn, has limited the selection of materials suitable for use as the inner layer.